Note the ball in this Ball Point plug from Bob’s collection. When the ball bounces, the plug fires.

Plugs with glass insulators from Bob’s collection. “When you fired the engine, you’d adjust the carburetor to get the right color showing in the visible plug,” Lanning says. “They say it looked like the Fourth of July when they were running.”

A trio of “window” plugs from Lanning’s collection. The opening allows a peek at the spark.

Bob’s Twin plug: When one end fouled, the plug could be flipped and re-used.

A French-made DeDion dating to the late 1890s is among the oldest spark plugs. This one (from Bob’s collection) was made for a three-wheel trike; it has never been used.

Bob’s Eyquem Nationale plug, commemorating the return of Alsace-Lorraine to the French.

A Jumbo Jiant from Bob’s collection.

Bob’s Nine Lives plug.

An Ouaka top primer plug.

A spark plug compression whistle. The modern spark plug comes in one piece. “Before World War II,” Lanning says, “you could take plugs apart and renew them with a new core.”

A Rawa primer plug made in Germany, one of only three known. The plug was one of the first Bob bought. “I had no idea what it was,” he says. “I stayed up half the night to get it off eBay.” He dates the piece (which has an ebony handle) to the years immediately preceding World War I.

At left: Lanning’s Mayo quick detachable plug. The plug could be removed without use of tools. Right: Lanning’s Maco dual primer plug. Commonly used in early fire trucks, the plug’s two sets of priming cups allowed quick and easy priming. “When you have to prime 12 cylinders, that made a difference,” Lanning says.

Spark plug boxes – like this one for the Montgomery Ward Leak Proof, from Lanning’s collection – are also collectible.